1. Field of the Invention
The present invention relates to an electron cyclotron resonance (ECR) apparatus used in etching and depositing steps in fabrication of a highly integrated semiconductor device, and more particularly to an ECR apparatus capable of achieving a cryogenic cooling effect.
2. Description of the Prior Art
Generally, ECR etching equipments utilizing plasma have a construction for receiving a substrate (wafer) in the process of fabrication of semi conductor devices, controlling parameters such as temperature and radio frequency required in an etching step so that the wafer can properly match to the etching step, and uniformly dropping ions and radicals participating in practical process steps so that they can react with desired targets to be processed. Such a construction involves important factors determining the superiority of etching equipments and affects considerably results of process steps. In particular, parameters determining etching rate, selectivity, anisotropy and uniformity, all of which are indicative of characteristics of etching equipments, are mainly affected by an electrode.
The electrode is a part having a close relationship with the carriage of the wafer. Accordingly, the electrode should be designed so as to safely seat the wafer thereon.
Processes for etching semiconductor elements are classified into a wet etching process using an acid and a dry etching process using plasma. For fabricating gates and trenches having microstructures, the dry etching process is used which provides a high anisotropy and a uniformity in etching rate and achieves a selective etch. As such a dry etching process, there have been known an ECR microwave plasma etching process and a reactive ion etching (RIE) process.
To achieve a high anisotropic etch at a high etch rate means that a conflicting increase/decrease effect present between the etching rate and the side wall etching is eliminated. The RIE process using radio frequency is adapted to achieve an anisotropic etch by utilizing a directional energy included in ions. When ions having an energy of a certain level strike against a substrate (wafer), a crystalline defect may occur at a film formed on the wafer or the wafer itself. When the ion energy is high, therefore, it is essentially required to mix a certain gas with the ions so as to reduce an undercut phenomenon occurring in the reactive ion etching.
In the RIE process, however, sufficiently high etch rate and selectivity can not be obtained. Furthermore, the RIE process requires an additional gas injection for a formation of a side wall protective film. As a result, the RIE process has problems of a complicated process, an increased wafer contamination, a degraded electrical characteristic of a device finally fabricated, and a decreased yield.
On the other hand, the ECR microwave plasma etching process has been developed to overcome the limitation of the above-mentioned RIE process. The ECR microwave plasma etching process generates a reduced contamination and a reduced crystalline defect because it is carried out under a pressure lower than that used in the RIE process.
Even in the ECR microwave plasma etching process, however, it is impossible to individually control the side wall etching and the substrate etching. Furthermore, a conflicting increase/decrease phenomenon typically present between the anisotropic etching and the etch selectivity occurs in both the RIE process and the ECR microwave plasma etching process.